C2MS13 — Re-evaluate Field Types in Message Header

In the Header, many fields are Subject Token String, but if they are never used in a subject, they could just be String. In 1.0 most of these were type Header String, later changed to STS, which might be why... could be someone just declared any string in the Header to be Header String type? Evaluate and change where appropriate.

This requires table and figure changes.

Fields for consideration are:

• MESSAGE-CLASS (Not used in Subject, but could be in 2.x?)
• FACILITY (FACILITY is never used in Subject. However, DESTINATION-FACILITY is, so probably keep it the same for consistency)
• CLASS (CLASS is not used in the Subject, but could be in 2.x? Doesn't seem to hurt)
• SUBCOMPONENT1/2 (COMPONENT is an element of the Subject, so while SUBCOMPONENT1/2 are not, it makes sense for consistency).